1. Technical Field
The present invention relates to a method and apparatus for remotely actuating a downhole device such as a packer. Specifically, the method involves the use of a resonant chamber to produce a signal detectable by a receiver/actuator coupled to the downhole device.
2. Description of the Related Art
The creation of an oil well involves two phases, drilling and completion. During the drilling of a well, a bit may be suspended along with related equipment from a drill string. The drill string is suspended from the crown block of a derrick by cables which bear a portion of the drill strings weight. The drill string and bit are rotated by a rotary table, driving the bit into the ground. A drilling mud can be circulated through the drill string to clean and cool the bit. The circulating mud also carries debris from the hole by way of the annulus between the drill string and the walls of the well. As the well becomes deeper, additional sections of drill string are added. Further, devices can be added to the drill string to help steer the bit or to perform early testing of the formation. If a well does not encounter commercial amounts of gas and oil, the well can be plugged and abandoned. However, if significant amounts of gas or oil are found, the well is completed.
During the completion of a well, casing can be cemented against the inside of the well to stabilize the wall of the well. A completion string can then be lowered into the cased well. The completion string can include packers to isolate specific portions of the well, perforation guns used to provide communication ports between the casing and surrounding formation, and other devices. Sometimes the downhole tools are actuated during the completion process. Other times, it is desirable to wait until the reservoir conditions merit the use of the specific tools. Therefore, a need exists for a method and apparatus to remotely actuate downhole tools during drilling, during completion, and after completion. It is important that such a method be non-interventional; in other words, nothing should have to be run into the well to actuate the downhole device.
U.S. Pat. No. 5,579,283 to Owens et al. and entitled "Method and Apparatus for Communicating Coded Messages in a Wellbore" discloses a method of impressing a command message upon a fluid column between a transmission node and a reception node. A transmission apparatus is in communication with the fluid column, for altering pressure of the fluid column to generate a portion of the coded message. A reception apparatus is provided at the reception node. The reception apparatus includes a rigid structural component with an exterior surface which is in direct contact with the fluid column and an interior surface which is not in direct contact with the fluid column, and a sensor assembly which detects elastic deformation of the rigid structural component. However, the well bore must contain only fluid of the same density to properly work. This might require the circulation of the drilling fluid to purge any gases.
A need exists for a method of remote actuation which allows an actuation signal to be transmitted down either an annulus or within the tool string. Such a device should be tunable to maximize the signal strength and to compensate for the geometry of the transmission path.